Three weeks barricaded inside a room without food, sleep or company. It sounds like the kind of thing you'd only put yourself through if you were quitting heroin or training to become a Zen monk. For Grimes, however, it's all part of the essential process of creating hypnotic weirdo pop.

"Once you hit day nine, you start accessing some really crazy shit," smiles Claire Boucher, the skittish 24-year-old Canadian behind the deliberately misleading Grimes moniker. "You have no stimulation, so your subconscious starts filling in the blanks. I started to feel like I was channelling spirits. I was convinced my music was a gift from God. It was like I knew exactly what to do next, as if my songs were already written."

Welcome to Grimes's world, where a voguish braindump of techno-mystical pop trash signifiers is given lift-off by Claire's insistence on pushing things a little bit further than your average blog idol. Her sleep-deprived, speed-fuelled working methods may sound extreme but it's hard to argue with the results. Grimes's recent third album, Visions, is a bewitching lo-fi blend of R&B melodies and new age atmospherics, fashioning flimsy components into something sensual and sweetly psychedelic.

It won Claire a deal with 4AD – appropriately enough, since Visions smoulders with the kind of necromantic charm that once powered label mainstays Cocteau Twins and Dead Can Dance. There are parallels, too, with Fever Ray and Björk in the way that Claire has assumed full control of her production, artwork and videos in order to further her eccentric vision.

Courted by fashion labels, she has appeared on the cover of Dazed & Confused dripping with Givenchy jewellery, despite the fact that her personal style is more Star Wars Cantina by way of the Sue Ryder shop. Today she's wearing a camo hoodie beneath a hand-me-down fur coat, accessorised with a multicoloured silk scarf, plastic shades, sky blue pumps and algae-green hair. It's a bold combo that would turn heads in dour downtown Montreal, although Claire looks perfectly at home among the junkshop flotsam and aborted art projects of La Brique, a former industrial loft that's now the epicentre of the city's colourful underground scene.

"From an early age I knew I would be unhappy if I wasn't doing something creative," she says, settling into an old wheelchair that constitutes La Brique's most comfortable seat. "It could have been art, it could have been architecture. I was always really into painting but I didn't feel like I would be able to do anything new, whereas with music there's still so much to be explored."

A former goth kid from Vancouver, Claire originally moved to Montreal to study Russian literature at McGill University, before switching to the neuroscience course. Music never seemed like a viable option until she started hanging out at La Brique's predecessor Lab Synthèse, where she was encouraged to produce her own tracks by her now-manager and engineer Sebastian Cowan. When Lab Synthèse's co-founder David Matthew Peet killed himself in 2008, she decided that she owed it to him to submit to her to true calling.

"I was like: 'Fuck, I could die. We could all die, at any time. Why the hell am I wasting my time? I'm just going to do what I want to do for the rest of my life. I don't need money.'" To the mild horror of her parents, Claire turned her back on the world of brain biology to pursue Grimes full time. "I've completely fucked my life," she admits cheerily. "I don't live anywhere, I don't see my friends. You have to sacrifice a lot of things to do this. But the pay-off is this incredible freedom."

Early Grimes releases showed hazy promise, even if they felt a little too much like scenester in-jokes (her 2010 debut Geidi Primes was cassette-only, full of references to 80s sci-fi film Dune). Claire's epiphany came when realised that she could make something more honest and universal if she confronted her own demons in her music.

'I eventually realised that by making songs I could work through these things that had been plaguing me for years'

Photograph: John Londono

"Visions was an extremely cathartic album to make. I went through a period a few years back when I was really addicted to drugs. Two of my best friends died, I had this really fucked-up assault experience and I was constantly in and out of terrible relationships. I never really dealt with all that, but I eventually realised that by making songs I could work through these things that had been plaguing me for years."

As a result, Claire reckons there is a "weird jubilance" to Visions. "It can totally be a party album if you want, which is hilarious to me because it's so tortured. But because it's about sloughing off that pain, there is a kind of joy in the way it takes you from utter depression to utter ecstasy."

She concedes that this narrative might be difficult to glean from her lyrics, which are generally elusive and impressionistic, shying away from specifics. "I feel Visions could go a lot further emotionally. It worked for me at the time but now it does seem like I was hiding. I definitely want the next record to be a lot more direct."

The names of Nine Inch Nails and notoriously uncompromising noise band Swans are mentioned. But then so is Michael Jackson. "I still want to make pop music," she assures. "I want the music to be more assaulting but more comforting at the same time." Claire gazes happily around the vibrant clutter of La Brique. "That's the basis of this whole Montreal scene. Everyone is really into pop music, everyone has a strong image and everyone is into branding. But everyone also does tons of drugs, makes really experimental music, does crazy shit and lives in a hovel with no heating."

"Branding" is a word Claire mentions often, with an enthusiasm that might offend preceding indie generations. "I used to think that focusing on the visual aspect was really vapid and ridiculous too," she admits, "but I've come to realise it's actually one of the most powerful tools I have to work with. The way that you present yourself visually totally dictates your audience and everything that anyone thinks about you. What's the difference between Napoleon and everyone else? Napoleon had great image branding. When people think of Napoleon they're not thinking of the Egyptian campaign or whatever, they're thinking of his fucking hat and his fucking hand in his waistcoat."

Yet despite her own version of the hat and the waistcoat – the dyed fringe, the occultish homemade tattoos – Claire insists that Grimes is not a kooky persona that she slips on and off with her rings. "That would be cheesy, and I'm really bad at faking it. If I'm a bad mood I can't go onstage and smile. Sometimes my show is really emotional and quiet and sometimes the same set is like a punk show where I turn up the distortion and scream."

Her gig the following night at Montreal's Cabaret Du Mile End is neither, although Claire's boisterous vocals betray her mixed emotions about hurtling off down a road that most of her friends in the audience will never get to travel. She arrives at the afterparty with the intention of getting wasted, but come 4am she's still perched on a pool table, deep in conversation with Win and Regine from Arcade Fire, receiving what looks suspiciously like the Canadian equivalent of the "Bono talk". Given her current trajectory, their advice may well come in handy.

More hot acts coming out of the Montreal music scene

Doldrums

Airick Woodhead AKA Doldrums is Grimes's brother from another mother. He guested on Visions, while his own music offers a more intense and unsettling version of Grimes's eldritch pan-global pop. He impressed Portishead so much with his cover of Chase The Tear that they released it themselves.

D'eon

Released the excellent split EP Darkbloom with Grimes last year, the cover showing the pair dressed as cave-dwellers. d'Eon's slick contributions explore the subject of communication breakdown via the medium of warped 80s R&B.

Majical Cloudz

"The most secretly prolific songwriter I know," says Claire of ex-boyfriend Devon Welsh, who makes lush, childlike dreampop under the name Majical Cloudz. Devon guested on Visions track Nightmusic, while Claire's vocals are all over last year's Majical Cloudz II.

Born Gold

Originally from Edmonton and previously labouring under the awful name Gobble Gobble, Born Gold doubled as Grimes's backing band on her North American tour. Their own brisk, ravey sets featured frontman Cecil Frena wearing a flashing LED suit.

Purity Ring

After signing Grimes, 4AD dove back into the Montreal scene to snap up Purity Ring, a duo formed by Born Gold's Corin Roddick and singer Megan James. Debut album Shrines is out in July, influenced by the gloopy swagger of Houston hip-hop.